The present invention relates to reflective liquid crystal display devices for direct view application used in wordprocessors, laptop personal computers, and other office machinery, as well as in a variety of visual and game machines, without a need for a backlight, and also relates to such reflective liquid crystal display devices incorporating a touch panel arranged therefrom.
Liquid crystal display devices, being characterized by their thinness and light weight, have successfully found commercial applications as color display devices. Among these color liquid crystal display devices, transmissive liquid crystal display devices provided with a light source for illumination from behind are in particularly widespread use, and are adopted for an increasingly wider variety of applications because of the above-mentioned features.
In contrast to the transmission liquid crystal display device, the reflective liquid crystal display device does not require a backlight for display, and therefore can reduce the power consumption of the light source. The exclusion of the backlight further characterizes the reflective liquid crystal display device by allowing it to be more compact and lightweight.
In other words, in comparison to conventional transmissive liquid crystal display, the reflective liquid crystal display device can lower the power consumption, and be suitably used in equipment which needs to be lightweight and thin. For example, if the equipment with the reflective liquid crystal display device is designed while retaining conventional operation time, the reflective liquid crystal display device can not only cut down on the backlight space and weight, but consumes less power, and becomes capable of running on a smaller battery, making it possible to further reduce the size and weight. If the equipment with the reflective liquid crystal display device is manufactured while retaining conventional size or weight, use of a larger battery is expected to increase operation time dramatically.
In addition, as to display contrast properties, the light emitting display device, such as the CRT, degrades greatly in contrast ratio when used outdoors during the daytime. Even the transmissive liquid crystal display device subjected to a low reflection treatment inevitably suffers similarly from greatly decreased contrast ratios when used in ambient light, such as direct sunlight, that is excessively strong compared to display light.
In contrast, with the reflective liquid crystal display device, the display light obtained is proportional to the amount of ambient light, which is an especially suitable feature for application in a personal digital tool, a digital still camera, a portable camcorder, and other devices that are often used outdoors.
When considering these potential application fields, the reflective color liquid crystal display device appears very promising; however, a relatively low contrast ratio and reflectance, as well as insufficient performances in multi-color, high precision, and moving picture display, have so far been obstacles in realizing commercially viable reflective color liquid crystal display device.
The following description will explain the reflective liquid crystal display device in further detail. The conventional twisted nematic (TN) type liquid crystal element includes two linear polarizer plates (hereinafter, will be simply referred to as polarizer plates), and therefore boasts an excellent contrast ratio and viewing angle dependency property; however, the reflectance is inevitably low. In addition, since the liquid crystal modulation layer is separated from the light reflective layer by a distance equivalent to the thickness of a substrate, etc., there occurs parallax due to a disparity between incoming and outgoing optical paths of illumination light. Therefore, especially in a typical arrangement used for transmissive liquid crystal display devices where a single liquid crystal modulation layer is combined with a color filter that includes a separate subpixel for each color element, provided that light does not travel parallel to the normal to the substrate, ambient light enters and exits after reflection through different color subpixels. This causes moire and other undesirable phenomena, rendering the transmissive liquid crystal display device unsuited for high resolution, high precision, color display use.
For these reasons, no reflective color display device using this display mode has so far been commercialized.
Meanwhile, Guest-Host type liquid crystal elements (hereinafter, will be abbreviated as GH) have been developed that uses no or only one polarizer plate and includes liquid crystalline material doped with dyestuff. However, the GH type liquid crystal element is not highly reliable due to the addition of the dye, and the low dichroic ratio of the dye cannot produce a high contrast ratio.
Among these problems, the insufficient contrast level in particular causes serious degradation in color purity and creates a need to incorporate a color filter of high color purity in a color display device using a color filter. This entails a problem of reduced brightness caused by the color filter of high color purity, and cancels to some degree the advantage of this mode that high brightness is achieved by use of no polarizer plates.
On these backgrounds, research and development is under way to successfully manufacture a liquid crystal display element in a mode in which a single polarizer plate is used (hereinafter, will be referred to as a single polarizer plate mode), which is highly promising to realize a high resolution and high contrast display.
Japanese Laid-Open Patent Application No. 55-48733/1980 (Tokukaisho 55-48733) discloses such an example of a liquid crystal display element of a reflective TN mode (45xc2x0-twisted type) using a single polarizer plate and a quarter-wave plate.
With this liquid crystal display device, black and white display is performed, using a 45xc2x0-twisted liquid crystal layer and controlling the electric field applied thereacross, by realizing two states, in one of which the plane of polarization of incoming linearly polarized incident light is parallel to the optical axis of the quarter-wave plate and in the other of which the plane of polarization forms 45xc2x0 with the optical axis of the quarter wave plate. The liquid crystal cell is structured to include a polarizer, a 45xc2x0-twisted liquid crystal cell, a quarter-wave plate, and a reflector plate, when viewed from the side at which light enters.
Further, U.S. Pat. No. 4,701,028 (Clerc et al.) discloses a liquid crystal display device of a reflective-type, homeotropic alignment mode wherein a combination of a single polarizer plate, a quarter-wave plate, and a perpendicularly aligned liquid crystal cell is used.
Meanwhile, the inventors of the present application filed an application for a reflective-type, parallel alignment mode wherein a combination of a single polarizer plate, a homogeneous alignment liquid crystal cell, and an optical retardation compensation plate is used (see Japanese Laid-Open Patent Application No. 6-167708/1994 (Tokukaihei 6-167708)).
This reflective liquid crystal display device includes a liquid crystal cell constituted by a homogeneously-aligned liquid crystal layer, a reflector plate (disposed inside the liquid crystal cell beneath the liquid crystal layer), a polarizer plate (disposed on the liquid crystal cell), and a single optical retardation compensator plate (placed between the liquid crystal cell and the polarizer plate). Further, according to this display mode, throughout the total length of the optical path, i.e., the incoming optical path and the outgoing optical path, light passes through the polarizer plate only twice and through the transparent electrode where light is inevitably absorbed on a glass substrate (top substrate) of the liquid crystal cell also only twice. Therefore, a high reflectance can be obtained by means of a reflective liquid crystal display device of this structure.
Further, Japanese Laid-Open Patent Application No. 2-236523/1990 (Tokukaihei 2-236523) discloses an arrangement in which a twisted nematic liquid crystal layer is interposed between a reflector plate (disposed inside a liquid crystal cell) and a single polarizer plate.
Further, Fourth Asian Symposium on Information Display (Chung-Kuang Wei et al., Proceedings of The Fourth Asian Symposium on Information Display, 1997, page 25; hereinafter will be abbreviated as ASID 97) discloses an arrangement wherein 90xc2x0-twisted nematic liquid crystal is interposed between a reflector plate disposed inside the cell and a combination of a quarter-wave plate and a polarizer plate which realizes a broad band display.
In addition, Japanese Laid-Open Patent Application No. 4-116515/1992 (Tokukaihei 4-116515) discloses a liquid crystal display device wherein incident circularly polarized light is used for display. In addition, as a method of obtaining circularly polarized light in a broad band of spectrum, Pancharatnam teaches the use of a plurality of optical retardation compensator plates in Proc. Ind. Acad. Sci. Vol. XLI, No.4, Sec.A, page 130, 1955.
The description below will explain display principles of a single polarizer plate mode employed in ASID 97 and in the Japanese Laid-Open Patent Applications No. 6-167708/1994, No. 2-236523/1990, and 4-116515/1992.
The polarizer plate disposed on the side where light enters serves to pass only one of the linearly polarized light components of the incoming and outgoing polarized light and absorb the other linearly polarized light component. The polarization state of the incoming light that has passed through the polarizer plate is then changed by an optical retardation compensator plate, such as a quarter-wave plate (in the cases of Japanese Laid-Open Patent Application No. 6-167708/1994 and ASID 97), or remains unchanged (in the case of Japanese Laid-Open Patent Application No. 2-236523/1990), and the light enters the liquid crystal layer. The polarization state is changed further as the light passes through the liquid crystal layer, before the light reaches a reflector plate.
Further, the light that has reached the reflector plate changes its polarization state in the reverse sequence to that of the incoming light: the light passes through the liquid crystal layer, the quarter-wave plate, etc. Consequently, the ratio of the linearly polarized light component in a transmission direction of the polarizer plate to the light obtained here will decide the total reflectance of the liquid crystal layer. In other words, the liquid crystal display element appears brightest when the outgoing light, immediately before passing through the polarizer plate, is linearly polarized in the transmission direction of the polarizer plate, and darkest when linearly polarized in the absorptive direction of the polarizer plate.
It is known that the necessary and sufficient condition for the light which enters and leaves the liquid crystal display device perpendicularly to the device to realize such a bright state is that the light be linearly polarized in an arbitrary direction on the reflector plate, and that for it to realize such a dark state is that the light be circularly polarized either right handed or left handed on the reflector plate.
Meanwhile, a touch panel, as well as a conventional keyboard, is a very useful input means incorporated in a personal digital tool. This is especially true in inputting such languages including Japanese that keyboard inputs need to be converted; with increasing information processing capability and newly developed software, the touch panel, which used to serve simply as a pointing device, now more typically plays a greater role as an input device such as a pen-based handwriting input device.
To realize this particular input method, the input device is disposed to overlap the front of the display device. However, since the reflective liquid crystal display device uses reflected light for display, the means to reduce reflection provided to the touch panel should not interrupt display image produced by the underlying reflective liquid crystal display device. For example, Japanese Laid-Open Patent Application No. 5-127822/1993 (Tokukaihei 5-127822) discloses that a touch panel, a quarter-wave plate, and a polarizer plate are stacked together to reduce reflection.
Among the aforementioned conventional techniques, the liquid crystal display device disclosed in Japanese Laid-Open Patent Application No. 55-48733/1980 is not suitable for a high resolution, high precision display, because despite the need to provide a quarter-wave plate between a liquid crystal layer and a reflector plate, it is difficult essentially to form a reflective film inside the liquid crystal cell.
In addition, the liquid crystal display device that operates in the homeotropic alignment mode disclosed in U.S. Pat. No. 4,701,028 has following problems. The homeotropic alignment, especially the inclined homeotropic alignment, is extremely difficult to control, and the control requires such a complex arrangement that is not suitable for mass production. Another shortcoming of the homeotropic alignment is its slow response.
In addition, coloring occurs with the aforementioned reflective-type parallel alignment mode due to small unevenness of the liquid crystal cell and the optical retardation compensator plate. The conventional arrangements, as discussed here, are likely to suffer from coloring in a dark state and failure to realize black and white display.
In addition, the arrangements disclosed in Japanese Laid-Open Patent Application No. 2-236523/1990 and Japanese Laid-Open Patent Application No. 4-116515/1992, although being capable of increasing the reflection in a bright state in comparison to the arrangement using two polarizer plates, still fail to realize a good black display due to great wavelength dependency of transmittance in a dark state.
In addition, ASID 97, although disclosing a display mode that enables a black and white display, does not disclose anything about the arrangement of the quarter-wave plate which is, described in this literature, to be fabricated for a broad band of spectrum.
In addition, according to a report made by Pancharatnam, three optical retardation compensator plates are required to obtain good circularly polarized light, which is not practical. In addition, detailed studies are yet to be made to combine this with liquid crystal display devices.
In contrast, the touch-panel-incorporating reflective liquid crystal display device, although its performance as a reflective liquid crystal display device has reached to a stage where it can be commercialized, still suffers from extremely poor visibility when used in a combination with a touch panel.
This is because, in the reflective display device, a single light source plays dual roles to cause reflection at the touch panel and to serve as a display light source for the display device, and decrease in visibility when used in a combination with a touch panel cannot be solved by removing the light that radiates from a light source (for example, a ceiling light) which cause reflection at the touch panel, or changing the direction of the light. This is a stark contrast to the transmissive liquid crystal display device and other light-emitting types of display devices with which this solution produces good results. A conclusion drawn from here is that the solution to the poor visibility is a key to a successful commercialization of the display device, as well as to that of a practical, low power consuming personal digital tool.
In addition, the arrangement of the touch panel disclosed in Japanese Laid-Open Patent Application No. 5-127822/1993 is effective in preventing reflection by means of the function of the quarter-wave plate; however, a typical quarter-wave plate is effective in preventing reflection only with respect to a particular wavelength in the visible range, and unavoidably less effective with respect to wavelengths that are immediately higher or lower than those particular wavelengths. Further, the brightness of a display is determined by a component of the polarized light that has travelled through the underlying display device, the component being in a transmission direction of a circular polarizer that is obtained as a combination of such a quarter-wave plate with a polarizer plate.
More specifically, when the underlying display device has substantially no polarization dependence (e.g., a white-Taylar type Guest-Host liquid crystal display device including dyestuffs added to its 360xc2x0-twisted liquid crystal), the reflection efficiency is, at maximum, half that of a display device having the same arrangement except that no touch panel is provided due to the transmittance of the polarizer plate placed on the front of the touch panel. Also, as another example, when the underlying display device utilizes linearly polarized light for a display (e.g., a TN or STN type liquid crystal display device including a polarizer plate further interposed in the space between the touch panel and the liquid crystal cell), the reflection efficiency is, at maximum, half that of a display device having the same arrangement except that no touch panel is provided. Further, in the last example, since the retardation caused by the quarter-wave plate depends on the wavelength of light, and the quarter-wave plate is sandwiched by polarizer plates, which causes tonal changes. In either case, brightness is insufficient, and is not suited for use in a combination with a reflective liquid crystal display device to which brightness improving means such as background light cannot be applied.
From what is laid above, it can be said that the touch panel described in Japanese Laid-Open Patent Application No. 5-127822 needs to be upgraded in its reflection preventing function. Additionally, the Laid-Open Patent Application does not disclose a suitable arrangement to utilize the daylight that has entered the touch panel for the reflective liquid crystal display device.
The present invention has objects to solve the aforementioned problems in a reflective liquid crystal display device of a single polarizer plate mode which can realize a high resolution display, and thereby to offer a reflective liquid crystal display device that boasts excellent visibility with a high contrast ratio and a capability to perform a color display, and to offer, through application of the reflective liquid crystal display device, a reflective liquid crystal display device incorporating a touch panel which maintains an enough level of display quality with a pressure sensitive input device being installed.
To achieve the foregoing objects, a reflective liquid crystal display device in accordance with the invention as defined in this application includes:
a liquid crystal layer sandwiched between a first substrate having a light reflexibility and a second substrate having a light transmissibility, the liquid crystal layer being composed of twist-aligned nematic liquid crystal having a positive dielectric anisotropy; and
circularly polarizing means, including a linear polarizer plate (hereinafter, will be simply referred to as polarizer plate), for selectively passing either right handed or left handed circularly polarized light out of natural light,
wherein the first substrate, the liquid crystal layer, and the circularly polarizing means are stacked in this order to form at least a part of the reflective liquid crystal display device,
the circularly polarizing means is disposed so that a major surface of the circularly polarizing means is on a liquid crystal layer side, the circularly polarized light exiting the circularly polarizing means through the major surface when natural light enters the circularly polarizing means,
the liquid crystal in the liquid crystal layer has a birefringence difference, which, if multiplied by a thickness of the liquid crystal layer, produces a product of not less than 150 nm and not more than 350 nm, and
the liquid crystal layer has a twist angle in a range of 45xc2x0 to 100xc2x0.
The reflective liquid crystal display device is a result of research and efforts by the inventors of the present invention. The inventors of the present invention have diligently worked on various reflective liquid crystal display devices of a single polarizer plate mode which can be arranged to be free from parallax, realize a high resolution display, and be electrically switchable between different polarization states on the reflector plate required to achieve a bright state and a dark state. As a result, the inventors of the present invention have found that by arranging a reflective liquid crystal display device so as to include circularly polarizing means and thereby produce a dark state in a state where a voltage is applied across the liquid crystal layer, a satisfactory dark state can be achieved without a need for high level precision in manufacturing processes of the liquid crystal layer.
The inventors of the present invention have further found that by thus designing the liquid crystal layer adopted in a reflective liquid crystal display device including circularly polarizing means that produces such a polarization state and realizes a satisfactory bright state in a low voltage state, the manufacture of the reflective liquid crystal display device is facilitated compared to the aforementioned conventional technologies.
In other words, according to the arrangement above, by adopting the circularly polarizing means and the liquid crystal layer and configuring the same as stipulated above, problems with conventional arrangements can be solved and a reflective liquid crystal display device with excellent display properties can be realized.
In addition, in the reflective liquid crystal display device, preferably, the circularly polarizing means includes: a first optical retardation compensator plate having a retardation in a substrate normal direction set to not less than 100 nm and not more than 180 nm; a second optical retardation compensator plate having a retardation in a substrate normal direction set to not less than 200 nm and not more than 360 nm; and a linear polarizer plate, the first optical retardation compensator plate, the second optical retardation compensator plate, and the linear polarizer plate being stacked in this order when viewed from the liquid crystal layer, and |2xc3x97xcex82xe2x88x92xcex81| has a value not less than 35xc2x0 and not more than 55xc2x0, where xcex81 represents an angle formed by a slow axis of the first optical retardation compensator plate and either a transmission axis or an absorption axis of the linear polarizer plate, and xcex82 represents an angle formed by a slow axis of the second optical retardation compensator plate and either the transmission axis or the absorption axis of the linear polarizer plate.
The inventors of the present invention have found that the preferred arrangement, when incorporated into the polarizer plate and the optical retardation compensator plate, enables the aforementioned polarization state to be obtained by means of the circularly polarizing means. With thus arranged circularly polarizing means, the light practically in the visible wavelength range of spectrum can be circularly polarized. Note that the transmission and absorption axes of the polarizer plate are mutually perpendicular.
In addition, in the reflective liquid crystal display device, preferably, the twist angle of the liquid crystal layer is in a range from 60xc2x0 to 100xc2x0, the product of the birefringence difference of the liquid crystal in the liquid crystal layer and the thickness of the liquid crystal layer is not less than 250 nm and not more than 330 nm, and either the transmission axis or the absorption axis of the polarizer plate forms an angle, xcex83, of not less than 20xc2x0 and not more than 70xc2x0, or not less than 110xc2x0 and not more than 150xc2x0 with an alignment direction of the liquid crystal molecules in a close proximity of the second substrate.
According to this arrangement, since the product of the birefringence difference of the liquid crystal in the liquid crystal layer and the thickness of the liquid crystal layer is great, more choices are available as materials for the liquid crystal and the thickness of the liquid crystal layer can be easily controlled, facilitating the manufacture of the device. Additionally, by setting xcex83 as above, a high quality reflective liquid crystal display device with suppressed contrast, coloring in a white display, and coloring in a black display can be obtained.
In addition, in the reflective liquid crystal display device, preferably, the first substrate having a light reflexibility includes a light reflective film, and the light reflective film has smooth and continuously changing concavities and convexities, and is made of a conductive material.
According to the arrangement, a diffuse reflector plate can be obtained that causes no unnecessary scattering and has no agitating function (light depolarizing function) to polarized light like a flat specular surface so as not to interfere with the reflectance modulation method whereby the reflective liquid crystal display device carries out a high resolution display. The obtained reflection property is effective by far, in comparison to a device including a non-diffusive, specular reflector plate and a scattering plate that is installed in front of a display device. In addition, since the light reflective film is made of a conductive material, the light reflective film doubles also as an electrode to apply voltage across the liquid crystal layer in collaboration with the transparent electrode of the second substrate.
Further, preferably, the concavities and convexities of the light reflective film have a direction dependent property that varies according to a direction on a substrate plane.
The preferred arrangement is a result of our finding that the mean cycle of the concavities and convexities provided on the light reflective film characterize the diffusive reflection property, and more specifically, enables the reflectance of illumination light that travels from a particular direction and is reflected in a particular direction to be increased, by uniformly setting the mean convex and concave cycle in any given direction on a plane of the reflector plate so that incident light is uniformly diffused, and modifying the cycle for a particular direction on the plane. The arrangement is especially effective when incorporated in a reflective liquid crystal display device in accordance with the invention as defined in this application which realizes a satisfactory dark state in comparison to Guest-Host mode, enabling even a brighter reflective liquid crystal display device to be obtained.
In addition, in the reflective liquid crystal display device, preferably, a single third optical retardation compensator plate or a plurality of the same is(are) provided between the circularly polarizing means and the liquid crystal layer to cancel a residual phase difference of the liquid crystal layer.
The preferred arrangement is made to eliminate residual phase difference, i.e., a light polarization modification function, that slightly remains in accordance with the component of the alignment of the liquid crystal that is parallel to the substrate, when the voltage applied across the liquid crystal layer has limitations and a maximum voltage is applied across the liquid crystal layer only to achieve a dark display. By canceling the residual phase difference by means of the third optical retardation compensator plate, a satisfactory black display is achieved at a practically maximum voltage. In addition, the same effects can be achieved by modifying the retardation of the second optical retardation compensator plate.
In addition, in the reflective liquid crystal display device, preferably, either the third optical retardation compensator plate or at least one of the third optical retardation compensator plates provided between the circularly polarizing means and the liquid crystal layer has an inclined optical axis, or a three-dimensionally aligned optical axis having therein a continuously varying inclined direction.
In a method to achieve a satisfactory dark display at a maximum value of an actual driving voltage and hence obtain a satisfactory display, cancelling the residual birefringence of the liquid crystal in a state where a substantial voltage is applied across the liquid crystal layer is effective, and to do this, it is possible to expand the viewing angle by expanding a viewing angle range in such a manner to satisfactorily cancel the residual birefringence of the liquid crystal layer.
To achieve this, in this arrangement, either the third optical retardation compensator plate or at least one of the third optical retardation compensator plates is designed with the three-dimensional configuration of the alignment of the liquid crystal taken into consideration. This enables a reflective liquid crystal display device having more satisfactory display properties to be obtained.
In addition, in the reflective liquid crystal display device, preferably, the first and second optical retardation compensator plates have such ratios of a refractive index anisotropy, xcex94n(450), with respect to light having a wavelength of 450 nm, a refractive index anisotropy, xcex94n(650), with respect to light having a wavelength of 650 nm, and a refractive index anisotropy, xcex94n(550), with respect to light having a wavelength of 550 nm that satisfy
1xe2x89xa6xcex94n(450)/xcex94n(550)xe2x89xa61.06 and
0.95xe2x89xa6xcex94n(650)/xcex94n(550)xe2x89xa61 respectively (the first arrangement), and more preferably,
1xe2x89xa6xcex94n(450)/xcex94n(550)xe2x89xa61.007 and
0.987xe2x89xa6xcex94n(650)/xcex94n(550)xe2x89xa61 respectively (the second arrangement).
According to the first arrangement, a highly practicable contrast ratio of 10:1 or larger can be achieved although there occur slight coloring in a bright state required of the reflective liquid crystal display device and reduction in contrast due to improvement of the reflectance in a dark state. Further, according to the second arrangement, a contrast ratio of 15:1 or larger can be achieved while successfully reducing coloring further in comparison to the first arrangement.
In addition, in the reflective liquid crystal display device, preferably, the twist angle of the liquid crystal layer is in a range of not less than 65xc2x0 and not more than 90xc2x0, the product of the birefringence difference of the liquid crystal in the liquid crystal layer and the thickness of the liquid crystal layer is not less than 250 nm and not more than 300 nm, and either the transmission axis or the absorption axis of the polarizer plate forms an angle, xcex83, of not less than 110xc2x0 and not more than 150xc2x0 with an alignment direction of the liquid crystal molecules in a close proximity of the second substrate (in contact with the second substrate).
According to the arrangement, the voltage to drive the liquid crystal layer can be further reduced, and a satisfactory white display can be achieved as well.
In addition, in the reflective liquid crystal display device, preferably, either the transmission axis or the absorption axis of the polarizer plate forms an angle, xcex83, of not less than 110xc2x0 and not more than 150xc2x0 with an alignment direction of the liquid crystal molecules in a close proximity of the second substrate, and a viewing direction is set to a direction on a plane that is defined by a normal to a display surface and a direction 90xc2x0 off the alignment direction of the liquid crystal molecules in a close proximity of the second substrate.
Similarly, in the reflective liquid crystal display device, preferably, either the transmission axis or the absorption axis of the polarizer plate forms an angle, xcex83, of not less than 20xc2x0 and not more than 70xc2x0 with an alignment direction of the liquid crystal molecules in a close proximity of the second substrate, and a viewing direction is set to a direction on a plane that is defined by a normal to a display surface and the alignment direction of the liquid crystal molecules in a close proximity of the second substrate.
According to the arrangement, by thus setting the viewing direction, a satisfactory visibility can be ensured. To put it differently, a satisfactory visibility can be obtained by setting xcex83 according to the viewing direction of the viewer. In addition, a satisfactory visibility can be obtained also by disposing, for example, a member for setting the viewing direction of the viewer on the display surface.
In addition, in the reflective liquid crystal display device, preferably, either the transmission axis or the absorption axis of the polarizer plate forms an angle, xcex83, of not less than 110xc2x0 and not more than 150xc2x0 with an alignment direction of the liquid crystal molecules in a close proximity of the second substrate, a viewing direction is set to a direction on a plane that is defined by a normal to a display surface and a direction 90xc2x0 off the alignment direction of the liquid crystal molecules in a close proximity of the second substrate, and the viewing direction is set to be on a plane that is defined by the normal to the display surface and a direction on a substrate plane in which the concavities and convexities of the light reflective film have a shorter mean cycle than in other directions.
Similarly, in the reflective liquid crystal display device, preferably, either the transmission axis or the absorption axis of the polarizer plate forms an angle, xcex83, of not less than 20xc2x0 and not more than 70xc2x0 with an alignment direction of the liquid crystal molecules in a close proximity of the second substrate, a viewing direction is set to a direction on a plane that is defined by a normal to a display surface and the alignment direction of the liquid crystal molecules in a close proximity of the second substrate, and the viewing direction is set to be on a plane that is defined by the normal to the display surface and a direction on a substrate plane in which the concavities and convexities of the light reflective film have a shorter mean cycle than in other directions.
According to the arrangement, a particularly excellent visibility can be obtained by further setting the direction in which the light reflective film, that is a diffuse reflector plate, is bright to the satisfactory direction described above. Note that the direction in which the diffuse reflector plate is bright, although being variable typically depending on the illumination direction and the direction of the viewer, can be accommodated satisfactorily under a variety of illumination conditions.
In addition, in the reflective liquid crystal display device, preferably, either the transmission axis or the absorption axis of the polarizer plate forms an angle, xcex83, of not less than 40xc2x0 and not more than 60xc2x0 with an alignment direction of the liquid crystal molecules in a close proximity of the second substrate, and the liquid crystal molecules in a close proximity of the second substrate form an angle xcex84 with a direction on a plane that is defined by a viewing direction and a normal to a display surface, the angle xcex84 being set to not less than 0xc2x0 and not more than 30xc2x0, or not less than 180xc2x0 and not more than 210xc2x0.
According to the arrangement, by thus setting the viewing direction, a satisfactory visibility can be ensured. To put it differently, a satisfactory visibility can be obtained by setting xcex83 and xcex84 according to the viewing direction of the viewer. In addition, a satisfactory visibility can be obtained also by disposing, for example, a member for setting the viewing direction of the viewer on the display surface.
In addition, a reflective liquid crystal display device incorporating a touch panel in accordance with the invention as defined in this application is a reflective liquid crystal display device incorporating a touch panel that comprises the reflective liquid crystal display device in accordance with the invention wherein a planar pressure sensitive element for detecting an external pressure is sandwiched with a layer-shaped empty space between the circularly polarizing means and the second substrate.
In the reflective liquid crystal display device in accordance with the invention as defined in this application, since the light is substantially circularly polarized after passing the circularly polarizing means, or the polarizer plate and the two optical retardation compensator plates, even if the light is reflected at the reflector plate in such a manner to contain no disturbance in the polarization state, the reflected light is absorbed by the polarizer plate before exiting the device. Therefore, reflected light does not degrade visibility with a pressure sensitive-type input device (touch panel) that is useful as an input device for a portable device.
Additional objects, advantages and novel features of the invention will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following taken in conjunction with the accompanying drawing or may be learned by practice of the invention.